Crystal structure determination and stability of copper (II) hydroxymethylphosphonate dihydrate

Copper(II) hydroxymethylphosphonate dihydrate HOCH₂PO₃Cu, 2 H₂O is triclinic : a = 10.870(3), b = 5.130(2), $\text{c}\text{= 5.628(2)}\text{A}\text{?}$, α = 96.6(1)β = 114.6(1), γ = 97.2(1)°, S.G. Pl?, Z = 2. The structure was solved by the heavy atom method and full matrix least-squares refinement to a final R value = 0.035. The two Cu atoms in the cell are structurally different : Cu(1) is octahedrally surrounded by four phosphonate oxygen atoms and two hydroxyl groups. Cu(1)O₆ octahedra chains extend along 010]. Cu(2) is coordinated to two phosphonate oxygen atoms and four water molecules. Cu(2)O₆ octahedra link the chains to form infinite layers parallel to 101]. These layers are held together by means of hydrogen bonds. The right formula must therefore be written Cu(HOCH₂PO₃)₂] Cu, 4 H₂O. The greater stability of the octahedral configuration versus the t.b.p. one and the occurence of bonding between copper atoms and hydroxyl groups can explain the increase of stability observed from methylphosphonate to hydroxymethylphosphonate copper complexes.